This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The Pikaard lab studies the ways genes are activated and repressed, using techniques of genetics, biochemistry and molecular biology. Our current research projects are focused on gene silencing and the role that chromatin proteins and small RNAs (siRNAs) play in these epigenetic phenomena. the research focuses on plants, the important one for this project is Arabidopsis thaliana. Inactive rRNA genes are silenced via chromatin modifications. rRNA gene silencing involves concerted changes in both DNA methylation and histone modification and we have proposed a model whereby DNA and histone modifications are each upstream of one another in a self-reinforcing, circular pathway. The Pikaard group wishes to identify the chromatin modifying activities involved in this repression cycle, using RNA-interference to knock down the expression of targeted genes. Two histone deacetylases, one DNA methyltransferase and several methylcytosine binding proteins have been identified in the screens thus far. We are making use of a variety of genetic, cytogenetic and biochemical approaches in order to understand the mechanism(s) of action of these chromatin modifying activities and to understand how their actions are intertwined to comprise an epigenetic on-off switch